The present invention relates to an aircraft with ventral fairing, as well as to a seal for such an aircraft.
It is known that certain aircraft, provided with a fuselage and with a fixed flying surface comprising two wings opposite one another with respect to said fuselage, comprise a cradle-shaped ventral fairing, generally projecting, which is fixed to the lower part of said fuselage at the crossover of the latter with said flying surface so as to shut off the landing gear bay by increasing possibly the bottomward volume thereof, and which possesses two longitudinal flanges climbing laterally along said fuselage, said flanges being provided, each, with an opening for the passage of the corresponding wing. Such a fairing supplements the aerodynamic profile of the crossover zone and its shape is tailored to minimize the aerodynamic drag to which it gives rise.
In certain known aircraft, the mode of fixing this ventral fairing to the fuselage entails the formation of a first peripheral slot around the ventral fairing, between the latter and the fuselage, and of a second peripheral slot around each wing, between the latter and the periphery of the corresponding opening of said fairing. In order to shut off said slots, an elongate seal is then provided, fixed to the periphery of said ventral fairing and to the periphery of each opening thereof.
It will be noted that, in addition to its leaktightness function, said seal must ensure the continuity of the surfaces so as to avoid the occurrence of significant drag and to absorb the relative movements between said fairing, on the one hand, and the flying surface and the fuselage, on the other hand.
To do this, the seals currently used comprise two longitudinal elastic lips able to be applied, via the inner face of their free end, respectively against the fuselage or the flying surface, one of these lipsxe2x80x94hereinafter designated the end lipxe2x80x94forming the free end edge of said seal, while the otherxe2x80x94hereinafter designated the inner lipxe2x80x94is carried by the inner face of this seal and is disposed set back with respect to said end lip.
Such a known seal exhibits numerous drawbacks. Firstly, during the fitting thereof, the inner lipxe2x80x94which is hidden by the seal itself and/or by the fairingxe2x80x94may turn over, its outer face then bearing on the fuselage or the flying surface instead of its inner face. In this case, the seal can no longer fulfill its function and it wears out very rapidly.
Additionally, in flight, on account of the pressure difference prevailing between the airfoil bottom surface (high pressure) and the airfoil top surface (low pressure) of the flying surface, a circulation of air is set up, between the airfoil bottom surface and the airfoil top surface of each wing, inside the fairing through said first and second slots, thereby causing, in particular on the airfoil top surface side, the detachment of the free end of said elastic lips of said seal, with respect to the fuselage or to the flying surface. Consequently, said elastic lips of the seal begin to vibrate, and do so within a frequency range which is perfectly audible from inside the cabin, this proving to be an inconvenience for the passengers. These vibrations are transmitted to the fuselage and to the elements which it comprises (floor, support, etc) and cause structural fatigue loading of said elements. Moreover, the vibrations, associated with the aerodynamic loads applied to said lips, give rise to their premature fatigue, this being manifested as rapid wear which may even result in their tearing. Finally, these vibrations bring about the occurrence of nuisance aerodynamic drag.
The object of the present invention is to remedy these drawbacks.
To this end, according to the invention, an aircraft comprising:
a fuselage and a fixed flying surface comprising two wings opposite one another with respect to said fuselage;
a cradle-shaped ventral fairing, fixed with play to the lower part of said fuselage, at the crossover of the latter with said flying surface and provided with two longitudinal flanges climbing laterally along said fuselage, said longitudinal flanges being provided, each, with an opening for the passage with play of the corresponding wing, in such a way as to form:
a first peripheral slot around said ventral fairing, between the latter and said fuselage; and
a second peripheral slot around each wing, between the latter and the periphery of the corresponding opening; and
an elongate seal, fixed to the periphery of said ventral fairing and to the periphery of each opening, so as to shut off said first and second slots, respectively, said seal comprising:
a longitudinal elastic end lip able to be applied, via the inner face of its free end, respectively against said fuselage or said flying surface; and
an additional longitudinal leaktightness member, carried by the inner face of said seal set back with respect to said end lip and also able to be applied against said fuselage or said flying surface, respectively,
is noteworthy in that said additional longitudinal leaktightness member is a radially elastic bead.
Thus, by virtue of the present invention, numerous advantages are obtained:
said radially elastic bead, carried by the inner face of the seal, is always correctly presented with respect to the fuselage or to the wings, during installation, being unable to turn over, as did the inner lip, which it replaces; and
said radially elastic bead, when it is applied against the fuselage or the flying surface of the aircraft, deforms and flattens, so forming a wide bearing surface, incapable of vibrating as did said inner lip. Moreover, this wide bearing surface ensures excellent leaktightness, so that the detachment and the onset of vibration of the free end of the end lip are if not completely eliminated, at least greatly reduced.
To reduce yet further, and even to completely do away with the vibrations of said end lip, it is advantageous, in accordance with another feature of the present invention, made possible by the fact of the excellent leaktightness afforded by said radially elastic bead, for said inner face of the free end of said end lip to comprise, at least on a part of said seal, at least one abutment boss, able to keep said end lip locally separated from said fuselage or from said wing, respectively, so as to contrive a controlled leakage of air which can pass through said first and second slots, in the case of a possible occasional and/or momentary defect of leaktightness of said bead.
Of course, the height of each boss and the number of said bosses, as well as their distribution, are determined, by calculation or by experiment, so that the leakage air flow rate between said bosses gives rise to little nuisance drag, while ensuring a low level of vibrations of said end lip of the seal.
Depending on the geometry of the fuselage, of the flying surface and of the ventral fairing of the aircraft, the pressure coefficient on the side of certain parts of the airfoil top surface of the wings may be very negative, this being representative of a very low pressure, so that any vibrations of the free end of the elastic end lip could, at these locations, have a large amplitude. It is therefore advantageous to apply the seal in accordance with the present invention at least facing said airfoil top surface parts at which the value of the pressure coefficient is strongly negative.
Of course, the present invention also relates to this kind of elongate seal for aircraft whose additional longitudinal leaktightness member is a radially elastic bead.
Moreover, the inner face of the free end of said end lip may comprise, at least on a part of said seal, at least one abutment boss, able to keep said end lip locally separated from the fuselage or from the flying surface, respectively, so as to contrive a controlled leakage of air which can pass through said first and second slots.
In order, at the same time, to ensure good presentation of said radially elastic bead during installation of the seal and good leaktightness of said seal after installation, it is preferable for the stiffness of said radially elastic bead to be greater on the side of the inner face of said seal than on the side of the free part of said seal able to be applied against said fuselage or the flying surface.
Accordingly, in particular, it is advantageous for said radially elastic bead to be tubular. In this case, in order to ensure correct bearing of said bead against the fuselage or the flying surface, it may be advantageous for the two lateral parts of said tubular bead, joining respectively the inner face of said seal to the free part of said bead which is able to be applied against said fuselage or the flying surface, to exhibit different stiffnesses.
Such variations in stiffness may be obtained through variations in constitutive material or through variations in thickness of the wall of said tubular bead, these variations in thickness possibly themselves resulting from the mutual off centering and/or mutual ovalization of the internal passage of the tubular bead with respect to the latter""s wall.
In a first embodiment, the seal in accordance with the present invention comprises a flat longitudinal part intended for the fixing of said seal to said ventral fairing and this flat longitudinal fixing part is disposed at the opposite end of said seal to said longitudinal elastic end lip, said radially elastic bead lying in an intermediate position between said longitudinal elastic end lip and said flat longitudinal fixing part. Such a seal is especially appropriate to the shutting off of said second slot between said ventral fairing and the flying surface.
As a variant, according to a second embodiment, the seal in accordance with the present invention likewise comprises a flat longitudinal part intended for the fixing of said seal to said ventral fairing, but this flat longitudinal fixing part is disposed in an intermediate position between said longitudinal elastic end lip and said radially elastic bead. The seal according to the invention is then especially appropriate to the shutting-off of said first slot between the ventral fairing and the fuselage.
Regardless of its embodiment, it is advantageous for the seal in accordance with the present invention to comprise a blade-shaped longitudinal recess made in the outer face of said flat longitudinal fixing part and serving as housing for the corresponding peripheral edge of said ventral fairing.
Preferably, the seal of the invention is made, by extrusion or by molding, in the form of a strip section or of a monolithic closed loop, for example made of a fiber reinforced elastomer.